Add EGLDevice backend to GLFW

This adds interface to graphics application to create EGLDisplay
directly over GPU device as enabled by EGLDevice extensions

Fixes #786.

src/egl_context.c

@@ -116,10 +116,18 @@ static GLFWbool chooseEGLConfig(const _GLFWctxconfig* ctxconfig,
         if (getEGLConfigAttrib(n, EGL_COLOR_BUFFER_TYPE) != EGL_RGB_BUFFER)
             continue;
 
+#if defined(_GLFW_EGLDEVICE)
+        // Only consider stream EGLConfigs
+        if (!(getConfigAttrib(n, EGL_SURFACE_TYPE) & EGL_STREAM_BIT_KHR))
+            continue;
+
+#else
         // Only consider window EGLConfigs
         if (!(getEGLConfigAttrib(n, EGL_SURFACE_TYPE) & EGL_WINDOW_BIT))
             continue;
 
+#endif
+
 #if defined(_GLFW_X11)
         // Only consider EGLConfigs with associated Visuals
         if (!getEGLConfigAttrib(n, EGL_NATIVE_VISUAL_ID))
@@ -376,6 +384,9 @@ GLFWbool _glfwInitEGL(void)
         return GLFW_FALSE;
     }
 
+// For EGLDevice backend the display gets initialized
+//  in _glfwPlatformInit()
+#if !defined(_GLFW_EGLDEVICE)
     _glfw.egl.display = eglGetDisplay(_GLFW_EGL_NATIVE_DISPLAY);
     if (_glfw.egl.display == EGL_NO_DISPLAY)
     {
@@ -396,6 +407,7 @@ GLFWbool _glfwInitEGL(void)
         _glfwTerminateEGL();
         return GLFW_FALSE;
     }
+#endif
 
     _glfw.egl.KHR_create_context =
         extensionSupportedEGL("EGL_KHR_create_context");
@@ -581,6 +593,9 @@ GLFWbool _glfwCreateContextEGL(_GLFWwindow* window,
         setAttrib(EGL_NONE, EGL_NONE);
     }
 
+// The surface for EGLDevice backened is created in _glfwPlatformCreateWindow
+//
+#if !defined (_GLFW_EGLDEVICE)
     window->context.egl.surface =
         eglCreateWindowSurface(_glfw.egl.display,
                                config,
@@ -593,6 +608,7 @@ GLFWbool _glfwCreateContextEGL(_GLFWwindow* window,
                         getEGLErrorString(eglGetError()));
         return GLFW_FALSE;
     }
+#endif
 
     window->context.egl.config = config;